1. Field of the Invention
The present invention relates to mechanical joints and robot wrists, and in particular, it relates to robot wrists capable of compound pitch/yaw motion with continuous roll rotation.
2. Description of the Prior Art
A number of robot wrist designs and drive mechanisms have been developed in trying to achieve a wrist having dexterity equal to the human wrist. An ideal wrist should have 180.degree. of singularity-free pitch/yaw motion with continuous roll rotation. A brief summary of some of the prior art wrists is given below.
A rotary actuator mechanism is described in the Higuchi et al U.S. Pat. No. 4,009,644. The rotary actuator of the Higuchi et al Patent is not very useful for the transmission of pitch, yaw and roll motion to a tool or implement member.
A number of robot joints are illustrated in the Vykukal U.S. Pat. No. 3,405,406 and the Vykukal et al U.S. Pat. No. 4,046,262. The Vykukal Patents describe hard-type space suits that permit the users inside the space suits to move around somewhat unrestricted.
The Bolner U.S. Pat. No. 3,912,172 describes a back-drivable, direct-drive hydraulically-actuated pitch and roll actuator.
The Rosheim U.S. Pat. Nos. 4,194,437 and 4,296,681, which were issued to the applicant of the present application, describe hydraulic servo mechanisms which impart rotary movements to a device to be driven.
The Stackhouse U.S. Pat. No. 4,068,536 describes a remotely-driven, mechanical manipulator. The manipulator is controlled by three concentric drive shafts which terminate in a spherically-shaped wrist mechanism.
The Totsuka U.S. Pat. No. 3,739,923 and the Niitu et al U.S. Pat. No. 3,784,031 describe a manipulator arm having two parallel rotating drive shafts in a beveled gear system which translates the drive shaft's rotating motion to a bending pitch motion and rotary roll motion in a tool member.
A mechanical wrist is described in German Patent 2,752,236 that includes three electric motors providing pitch, yaw and roll, which are mounted on the outside of a housing with the inside of the housing being hollow. The wrist is used for holding welding tongs and the hollow inside housing permits electrical power lines to be fed through the wrist.
The Molaug U.S. Pat. No. 4,107,948 describes a flexible robot arm that is composed of a number of mutually connected rigid links being connected at one end to a drive means and at the other end to a tool member.
Another robot arm is illustrated in the Wells U.S. Pat. No. 3,631,737. The robot arm of the Wells Patent includes a plurality of rigid tubular sections joined end-to-end by flexible joints to form an articulated arm. The rigid sections are manipulated by slender control cables which are attached to the respective sections and selectively extend and retract.
In addition, a number of well known universal joints are illustrated and described on pages 16 and 17 of the Pictorial Handbook of Technical Devices by Pete Grafstein and O. Schwarz, published by the Chemical Publishing Company, Inc. of New York, 1971. Although rotational motion can be transmitted through the universal joints illustrated on pages 16 and 17, the universal joints cannot be used in operations for transmitting pitch, yaw and roll motion to an implement or a tool member.
The development of robot arms and wrists is discussed in an article entitled, "Robot Wrist Actuators," Robotics Age, November/December 1982, pages 15-22 written by the applicant of the present invention. In this article, several characteristics are described which make robot wrists attractive. Disadvantages of prior art wrists are also discussed in the article.